1. Field of the Invention
This invention relates to a motorized window blind, more particularly to a motorized window blind which has telescopically fitted tubes driven by a motor to extend and retract a blind screen.
2. Description of the Related Art
Referring to FIG. 1, a conventional window blind 1 is shown to include a mounting frame 11, and a blind screen 10 which has a mounted end secured on the mounting frame 11, a liftable end 12, and an intermediate portion with a plurality of sheet portions 101. Right and left guiding threads 111, 112 have ends which are connected to a spring 13 received in the mounting frame 11, and weave through the sheet portions 101 via holes 113 formed therein. The other end of the left guiding thread 111 passes through a left friction member 14, and then extends along the liftable end 12 to enter a right friction member 15 so as to be fixed on a right fixing member 17. Likewise, the other end of the right guiding thread 112 passes through the right friction member 15, and then extends along the liftable end 12 to enter the left friction member 14 so as to be fixed on a left fixing member 16. By means of the friction of the friction members 14, 15, the liftable end 12 can be moved manually to extend and retract the blind screen 10, and can be maintained at a predetermined level.
However, when the conventional window blind 1 is mounted on a relatively high window, the moving operation of the liftable end 12 is difficult to conduct.